The present invention relates to a developing method and, more particularly, to a developing method for preventing developing a developing solution from remaining on the backside surface of a wafer.
The photolithography technique has broadly been applied in the manufacture of a semiconductor device. The principal steps of the photolithography process are as follows. First, a photoresist is coated on one surface of a wafer, then, a pattern is transferred to the photoresist and a developing process is performed. In the developing process, it is essential to send a wafer having exposed photoresist to a developing coating apparatus. FIG. 1 illustrates the structure of a traditional developing coating apparatus. As shown in FIG. 1, the traditional developing coating apparatus mainly comprises a spin chuck 11, a cup 12, an outer wall 13, a developing solution nozzle 14 and washing solution nozzles 15, 17. The spin chuck 11 is disposed in a reaction space of the developing coating apparatus, and the spin chuck 11 is equipped with a vacuum pump, not shown, for retaining the wafer 2 on the spin chuck 11. Additionally, the spin chuck 11 is connected to a rotation shaft of a motor, not shown, and raised or lowered by an elevator or lift mechanism. The motor, the elevator mechanism and the vacuum pump are all connected to an outer controller, not shown, for operating and controlling the spin chuck 11. The outer wall 13 surrounds the spin chuck 11 to form a reaction space. An exhaust passage 16 is placed at the bottom of the outer wall 13. The cup 12 is disposed in the reaction space formed by the outer wall 13 wherein the spin chuck 11 is disposed substantially in the center of the reaction space. Further, the cup 12 has a first inner wall 121 and a second inner wall 122. As a result, there is a ring groove 123 formed between the first inner wall 121 and the second inner wall 122. The developing solution nozzle 14 and the first washing solution nozzle 17 are disposed on the upper side of the spin chuck 11 for providing the required developing solution and washing solution respectively to the wafer 2 in the developing process. The second washing solution nozzle 15 is disposed on the cup 12 and near the second inner wall 122 for providing the washing solution to wash the backside surface of the wafer 2.
In some embodiments of the developing processes, the washing solution, e.g., pure water substantially, sprayed by the washing solution nozzle cannot totally remove the remaining developing solution on the backside surface of the wafer 2. The main reason is that the first inner wall 121, the second inner wall 122 and the ring groove 123 cannot completely prevent the developing solution from flowing through the gap between the backside surface of the wafer 2 and the cup 12, whereby a portion of the developing solution will still remain on the backside surface of the wafer 2. Although the conventional method employs the second washing solution nozzle 15 to wash the backside surface of the wafer 2, the washing solution sprayed by the second washing solution nozzle 15 still cannot wash the remainder of the developing solution while the developing solution passes the second washing solution nozzle 15 and flows into the spin chuck 11. It results in the dead zone for washing. Using only the second washing solution nozzle 15 to wash the contamination on the backside surface of the wafer will cause the outer-radiating water mark at the edge of the backside surface of the wafer. It leads to not efficiently preventing the contamination remainder.
In order to further reduce the problem of developing solution remaining on the backside surface of the wafer, there are some prior arts proposed but the efficiency is still limited. For example:
(1) Checking and Washing Step by Step
The method requires each wafer to be taken out for inspection after the developing process is completed. If it has contamination remaining on the wafer, the backside surface of the wafer would be washed again and again. Nevertheless, it often washes the wrong surface if operators have a misoperation, and then the circuits of the normal surface of the wafer will be destroyed. Moreover, the contamination on the backside surface of the wafer will be misjudged or missed if the wafer is inspected only visually. It may adversely affect the subsequent processes.
(2) Reducing the Supply Quantity of the Developing Solution
This method reduces the quantity of the developing solution flowing to the backside surface of the wafer. However, the process quality of the wafer will be influenced as the quantity of the developing solution is reduced to a specific value. As a result, it is hard to control an adequate quantity of the developing solution.
(3) Improving the Developing Coating Apparatus
The method emphasizes the hardware design of the developing coating apparatus. For example, the design may adjust the gap of the cup 12 between the first inner wall 121 and the backside surface of the wafer 2. Yet it may cause the developing solution to flow backward and pollute the backside surface of the wafer 2. If the quantity of the developing solution is sufficiently large, the gap still cannot prevent the developing solution from flowing through the gap between the first inner wall 121 and the wafer 2. Although the ring groove 123 between the first inner wall 121 and the second inner wall 122 can block portion of the developing solution, the excess developing solution will still further pass the second washing solution nozzle 15 and flow into the spin chuck 11 as the quantity is sufficiently large. If the developing solution flows into the spin chuck 11, the second washing solution nozzle 15 cannot work well. It leads to the dead zone for washing.
(4) Improving the Process
Although the adequate parameters can be obtained from the process, it would not still prevent the developing solution from remaining on the backside surface of the wafer for the wrong parameters used by the operator and the same parameters used in a different developing coating apparatus.
Therefore, how to provide a developing method to avoid the abovementioned disadvantages and prevent the developing solution from remaining on the wafer 2 efficiently is an important problem to solve.